1. Field of the Invention
The present invention relates to a cap with valve, such as a fuel cap installed to a fuel supply inlet that extends from a fuel tank of an automobile.
2. Description of the Prior Art
Conventionally, a cap with valve, for example, a fuel cap to be installed to a filler neck of a fuel tank is comprised of a cap body, a flange portion extending from the upper portion of the cap body outwardly in the radial direction, and a doughnut-shaped gasket disposed on the lower or sealing surface of the flange. The fuel cap is designed to cover a fuel supply inlet extending from the fuel tank while screwed into the fuel supply inlet (see Japanese Patent Unexamined Publication No. 111669/1989).
The conventional cap body has an upper portion and a threaded cylindrical portion attached to one of the upper portion for threadedly engaging the female threads of the fuel supply inlet.
The gasket is brought into pressure contact with both the sealing surface of the flange portion and an end surface of the fuel supply inlet when the cap body is screwed into the fuel supply inlet, thus sealing the fuel supply inlet hermetically.
However, in the conventional fuel cap, when the cap body is made from synthetic resin, the cap body must be formed by splitting its outer circumference into two parts in order to separate the mold, e.g., in the radial direction, because the cap body has a male thread on the threaded cylindrical portion.
As a result, parting lines are drawn not only on the outer surface of the cap body but also on the sealing surface of the flange portion.
Since the presence of the parting line on the sealing surface of the flange portion affects the gasket's sealability, the sealing surface of the flange portion must typically be ground to remove the burr after having been formed, hence increasing the number of manufacturing steps as well as the manufacturing cost of the fuel cap.
The above problems likewise occur in the case where the flange portion of the fuel cap is made of metal. Frequently, metal fuel caps contain burrs or other irregularities which the standard gasket is unable to seal. The end of the fuel supply inlet also frequently has burrs causing problems for the conventional gasket.